Nanowire- based solar cell structure

Abstract

The solar cell structure according to the present invention comprises a nanowire ( 205 ) that constitutes the light absorbing part of the solar cell structure and a passivating shell ( 209 ) that encloses at least a portion of the nanowire ( 205 ). In a first aspect of the invention, the passivating shell ( 209 ) of comprises a light guiding shell ( 210 ), which preferably has a high- and indirect bandgap to provide light guiding properties. In a second aspect of the invention, the solar cell structure comprises a plurality of nanowires which are positioned with a maximum spacing between adjacent nanowires which is shorter than the wavelength of the light which the solar cell structure is intended to absorbin order to provide an effective medium for light absorption. Thanks to the invention it is possible to provide high efficiency solar cell structures.

1 - 21 . (canceled) 
   
   
       22 . A solar cell structure comprising
 at least one nanowire that constitutes a light absorbing part of the solar cell structure; and   a light guiding shell that encloses at least a portion of the nanowire and is adapted to direct incoming light along the nanowire and through the light absorbing part of the solar cell structure.   
   
   
       23 . The solar cell structure according to  claim 22 , wherein the nanowire is made of a material with a direct bandgap. 
   
   
       24 . The solar cell structure according to  claim 22 , wherein the light guiding shell is made of a material with a higher bandgap than the segment. 
   
   
       25 . The solar cell structure according to  claim 22 , wherein the light guiding shell is made of a material with an indirect bandgap. 
   
   
       26 . The solar cell structure according to  claim 22 , wherein the nanowire comprises at least one segment made of a material with a first bandgap that is adapted to absorb light in a wavelength region of the solar spectrum with photons having a larger energy than the first bandgap. 
   
   
       27 . The solar cell structure according to  claim 26 , wherein the segment comprises a pn-junction. 
   
   
       28 . The solar cell structure according to  claim 26 , wherein the nanowire comprises a plurality of segments and each segment has a different bandgap in order to absorb light in different wavelength regions of the solar spectrum. 
   
   
       29 . The solar cell structure according to  claim 28 , wherein the plurality of segments is arranged so that the different bandgaps of the segments decrease in a direction away from intended incoming light and along the nanowire. 
   
   
       30 . The solar cell structure according to  claim 28 , wherein the segments are connected in series by means of Esaki diodes. 
   
   
       31 . The solar cell structure according to  claim 28 , wherein the segments are connected in series by means of metallic segments. 
   
   
       32 . The solar cell structure according to  claim 22 , wherein the light guiding shell is sufficiently narrow to allow only single-mode light propagation and the nanowire diameter is smaller than the light guiding shell thickness. 
   
   
       33 . The solar cell structure according to  claim 22 , wherein a width of the light guiding shell is larger than a wavelength of the incoming light divided by a refractive index of the light guiding shell. 
   
   
       34 . The solar cell structure according to  claim 22 , wherein the substrate comprises a photodiode structure formed by oppositely doped regions in the substrate adjacent to the nanowire. 
   
   
       35 . The solar cell structure according to  claim 22 , wherein the nanowire protrudes from a substrate. 
   
   
       36 . The solar cell structure according to  claim 22 , wherein an outer shell layer with passivating and insulating properties encloses the light guiding shell. 
   
   
       37 . The solar cell structure according to  claim 22 , wherein the light guiding shell is epitaxially connected to the nanowire. 
   
   
       38 . The solar cell structure according to  claim 22 , wherein a top portion of the nanowire extends from the light guiding shell, and a front contact encloses the top portion. 
   
   
       39 . The solar cell structure according to  claim 22 , comprising a plurality of nanowires which are positioned with a maximum spacing between adjacent nanowires which is shorter than the wavelength of the light which the solar cell structure is intended to absorb. 
   
   
       40 . A solar cell structure comprising a plurality of nanowires that each constitutes a light absorbing part of the solar cell structure and a maximum spacing between adjacent nanowires is shorter than the wavelength of the light which the solar cell structure is intended to absorb such that incoming light will experience an effective medium. 
   
   
       41 . The solar cell structure according to  claim 40 , wherein each nanowire comprises a plurality of segments and each segment has a different bandgap in order to absorb light in different wavelength regions of the solar spectrum and the plurality of segments is arranged so that the different bandgaps of the segments decrease in a direction away from intended incoming light and along the nanowire. 
   
   
       42 . The solar cell structure according to  claim 41 , wherein the maximum spacing between adjacent nanowires is shorter than 400 nm. 
   
   
       43 . The solar cell structure according to  claim 42 , wherein the maximum spacing between adjacent nanowires is shorter than 150 nm.